microGPS: On-orbit Demonstration of a New Approach to GPS for Space Applications

Jeffrey Srinivasan, Yoaz Bar-Sever, Willy Bertiger, Stephen Lichten, Ron Muellerschoen, Timothy Munson, Donovan Spitzmesser, Jeffrey Tien, Sien-Chong Wu, Lawrence Young

Abstract:	In February 1998 the Student Nitric Oxide Explorer (SNOE) was successfully launched and began scientific observations. In addition to three instruments designed by the University of ColoradoÕs Laboratory of Atmospheric and Space Physics to study Nitric Oxide in the atmosphere, the spacecraft also carried a 600 gram GPS receiver designed and built by the Jet Propulsion Laboratory. This receiver, known as microGPS, is a combination of simple low-power hardware and portable, efficient software that has been developed by JPL for spacecraft navigation in Earth orbit. It is intended for micro- and nano-satellite applications where mass and power budget margins are especially limited or as a robust second string to a conventional GPS receiver onboard any satellite. The microGPS hardware consists of lightweight antenna/receiver electronics that acquire occasional samples of GPS signals while consuming an average power of less than 100 milliwatts. Peak power is 875 milliwatts. The samples are stored in the microGPS for subsequent processing. Because it employs a sparse sampling technique, the microGPS has applications in tumbling/spinning satellites for routine navigation as well as in safe-hold recovery for any satellite whose orientation is unknown. In order to offer maximum flexibility in satellite design, the microGPS orbit determination software is designed for execution either onboard the spacecraft or on the ground. In the latter case, which was employed for the SNOE mission, the sparse GPS samples are telemetered to the ground and processed in post real-time to produce spacecraft orbits that can be uploaded to the satellite and projected ahead for real-time use. Onboard the spacecraft, the software could execute in the flight computer or in a special-purpose processor within the microGPS hardware unit (with slight increases in mass and power consumption). This paper will describe on-orbit operational experience with the microGPS receiver on the SNOE spacecraft as well as preview the next generation, dual-frequency microGPS receiver to be launched in mid 1999 on STRV- 1c, a geostationary transfer orbit spacecraft. Comparisons will be made between expected performance of the microGPS and actual observations. The design, expected and actual performance of the orbit determination software, which is rooted in the techniques and algorithms pioneered in JPLÕs high accuracy GIPSY/OASIS II software, will also be described.
Published in:	Proceedings of the 11th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1998) September 15 - 18, 1998 Nashville, TN
Pages:	1537 - 1545
Cite this article:	Updated citation: Published in NAVIGATION: Journal of the Institute of Navigation
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